This invention relates in general to chucks for holding articles for machining and in particular to a new and useful power driven chuck having centrifugal force compensating arrangement.
The invention concerns a power operated chuck for lathes with radially shiftable base or clamping jaws which can be driven by means of key bars guided in the clamping body tangentially to its axis of rotation in receiving pockets, where the key bars can be actuated jointly by an axially displaceable shifting member cooperating with wedge-shaped surfaces or the like, and engage a toothing of the jaws with serrated borders.
A chuck of this type, which works extremely well in practice, is known from German AS 25 56 227. Though this chuck comprises only a few parts, and is thus trouble free and economical to manufacture, it was found that particularly in the application to numerically controlled machine tools, the inwardly directed tension is reduced at high speeds. This is because the outwardly directed centrifugal forces generated by the jaws act against the jaws, and the forces add up in an internal stress and thus with outwardly directed tension, since there is no compensation of the centrifugal force.
Furthermore, hydraulically operated wedge hook chucks are known where the centrifugal force is compensated. To this end are provided compensating elements guided in the clamping body as counterweights, which are operatively connected with the jaws over toggle joints, likewise supported in the clamping body. Apart from the fact that such chucks are large in axial directions, a great disadvantage is that the static stresses acting on a clamped workpiece are sometimes quite different before and after a machining operation. During a revolution of the chuck, the tension transmitted by the shifting member to the jaws is practically completely compensated by the centrifugal force generated by the jaws. In this operating state, the tension is therefore produced by the compensating elements which are connected with the jaws by the guide levers. The shifting element connected over wedge-shaped surfaces with the jaws is thus relived, so that the jaws are shifted, though slightly, by the force still acting on them. When the chuck is stopped, its jaws are retained in this position, since the pressure medium acting on the shifting element is incompressible, so that a higher tension now acts on the workpiece, compared to the first clamping. Since the increase in tension can be quite considerable, this leads frequently to deformation of the clamped workpiece and also of the clamping body.